In the field of data storage, there are two main types of storage elements. The first type is volatile memory, in which information is stored in a particular storage element and the information is lost the instant the power is removed from the circuit. The second type is a non-volatile storage element, in which the information is preserved even when the power is removed. Of the second type, some designs allow multiple programming while other designs allow only one-time programming. Typically, the manufacturing techniques used to form non-volatile memory are quite different from standard logic processes, thereby dramatically increasing the complexity and cost.
Typically, one-time-programmable (OTP) memory devices include metal fuses, gate oxide fuses, etc. Metal fuses, as the name suggests, use metal fuses as programming elements. Gate oxide fuses include gate oxides as programming elements.
Conventional OTP memory devices were typically fabricated using aluminum interconnect technologies, which involve aluminum deposition, patterning, and etching, and thus are not compatible with current copper damascene processes, which have become standard processes. In addition, conventional OTP memory devices require either high voltage (such as gate oxide fuses) or high current (such as metal and via anti-fuses) for programming. Such high voltage or high current requirements need to be taken into design considerations, and thus the complexity and the cost of fabricating integrated circuits increases accordingly.
A logic-process-compatible one-time-programmable memory device is therefore highly desirable. Particularly, to be fully compatible with existing CMOS integrated circuits, the high programming current and/or high voltage requirements need to be lowered.